Hydrocarbon-Degradation by Acidophilic Microorganisms
Bio-filtration of volatile hydrocarbons and mineral oxidation in association with coal mining and oil seepages can lead to the simultaneous occurrence of strongly acidic conditions (pH < 4) and hydrocarbons. This chapter describes the current knowledge
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K. N. Timmis (ed.), Handbook of Hydrocarbon and Lipid Microbiology, DOI 10.1007/978-3-540-77587-4_140, # Springer-Verlag Berlin Heidelberg, 2010
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Hydrocarbon-Degradation by Acidophilic Microorganisms
Abstract: Bio-filtration of volatile hydrocarbons and mineral oxidation in association with coal mining and oil seepages can lead to the simultaneous occurrence of strongly acidic conditions (pH < 4) and hydrocarbons. This chapter describes the current knowledge on the taxonomy, ecology, physiology, biochemistry and genetics of hydrocarbon-degrading acidophiles. Knowledge is still sparse, so far only five bacterial and nine fungal acidophilic hydrocarbon-degraders have been described, in limited detail. Most bacterial hydrocarbondegraders are tolerant to high concentrations of heavy metals. The limited knowledge appears to relate to difficulties in obtaining pure cultures and the low effort so far put in microbiological characterization of hydrocarbon-containing acidic environments.
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Introduction
Oxidation of minerals, such as pyrite, is often accompanied by soil acidification, and can be due to natural (e.g., volcanic activity) and human-activity associated processes (e.g., mineral and coal mining). Mineral oxidation in association with coal mining and oil seepages can lead to the presence of hydrocarbons in acidic environments and the requirement for bioremediation. This chapter describes the taxonomy, physiology, biochemistry, genetics and ecology of acidophilic hydrocarbon degraders. Acidophiles are microorganisms metabolically active in strongly acidic environments (pH < 2.0). As the number of described microorganisms capable of degrading hydrocarbons at a pH below 2.0 is very limited, this chapter will also include microorganisms capable of hydrocarbon-degradation at a pH lower than 4.0.
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Taxonomy and Phylogeny of Hydrocarbon-Degrading Acidophiles
Acidophilic hydrocarbon-degraders are found among Bacteria and Eukarya, so far no hydrocarbon-degrading acidophilic Archaea have been isolated. While microorganisms have been isolated from hydrocarbon containing acidic environments, often the isolation conditions (pH, hydrocarbons as source of carbon) were not representative for the in situ conditions. For example, Dore et al. (2003) isolated five naphthalene-degrading strains from an acidic coal pile, of which only one was capable of growing at a pH below 4. Only a few bacterial isolates are currently known to grow with hydrocarbons below a pH of 4. 16S rRNA gene based phylogenetic information is available for five bacterial isolates (> Table 1). Gemmell and Knowles (2000) obtained 23 acidophilic, hydrocarbon-degrading isolates, however the 16S rRNA gene was sequenced for only two of these isolates (Acidocella sp. WJB-3 and Acidocella sp. LGS-3; > Table 1). The five bacterial isolates are associated with two phyla, four with the Proteobacteria and one with the Actinobacteria. The Proteobacteria isolates all belong to the Acetobacteraceae (Rhodospirillales, Alphaproteobacteria), which contains several
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